Liquid presence and temperature switch



M h 1965 J. B. BRENNAN ETAL 3,171,934

LIQUID PRESENCE AND TEMPERATURE SWITCH Filed March 14, 1965 Z INVENTORS United States Patent M 3,171,934 LIQUID PRESENCE AND TEMPERATURE SWITCH John B. Brennan and William L. Bleicher, Flint, Mich, assignors to General Motors Corporation, Detroit, Mich, a corporation of Delaware Filed Mar. 14, 1963, Ser. No. 265,161 Claims. (Cl. 280-138) This invention relates to switches and more particularly to a switch for imparting a signal when a liquid is not present or when that liquid has acquired a predetermined temperature.

Insofar as internal combustion engines are concerned, it has become desirable to discern the presence as well as the temperature of the engine coolant by the use of one device. Heretofore, a bimetal switch has been used which is grounded from one terminal below 120 F. and open when the coolant is above 120 F. The same switch has included another terminal which has shorted to ground when its bimetal is heated to 220 F. Sometimes, however, the bimetal becomes cooler when the coolant level drops below the zone of sensing despite boiling of the coolant so engine damage may occur before the operator is aware of the situation.

An object of the present invention is to provide a switch which will be capable of imparting a signal that a liquid such as an engine coolant is absent from a sensing zone or has attained a predetermined temperature at that zone and which will do so promptly when either condition becomes existant.

A feature of the present invention is a switch having two heat conducting probes, a heater coil in heat exchange with one of the probes and two bimetallic contact elements influenced by the temperature of the probes and adapted to carry a signal current when the probes become heated due to the absence of a liquid or attainment of a predetermined temperature by that liquid.

These and other important features of the invention will now be described in detail in the specification and then pointed out more particularly in the appended claims.

In the drawings:

' FIGURE 1 is a sectional view of a switch forming a preferred embodiment of the present invention;

FIGURE 2 is a sectional view looking in the direction of the arrows 22 in FIGURE 1 and a signal circuit being shown diagrammatically associated with the switch; and

FIGURE 3 diagrammatically shows a preferred signal circuit.

In FIGURE 1, a metal casing is depicted at and which is recessed at 12 to enclose two plastic or insulator members 14 and 16, a resilient gasket 18 interposed be tween the two members, and a second resilient gasket 20 retained between the member 16 and the bottom Wall 22 of the recess 12. The top peripheral edge of the member 10 is spun over as at 24 tightly to maintain the assembly.

The insulator member 14 has a top or small diameter chamber 26 in communication with a larger diameter chamber 28. Protruding from the member 14 are two spaced terminals 30 and 32 so placed as to extend from the chamber 28 and the upper or one end of the casing 10. The terminals 38 and 32 are epoxied in place after final assembly because they are riveted to the member 16 and then member 14 is pushed down over them. They are then sealed after replacing air in the chamber 26 with dry air to reduce moisture problems.

The insulator member 16 has a reduced diameter portion 34 in which are cast or molded two tubular copper probes 36 and 38 in such a way as to extend into the chamber 28 and also beyond the lower end 41) of the por- Patented Mar. 2, 1965 tion 34. The opposite ends of the probe 36 are compressed to retain one end of a bimetallic contact element 42 and one end of a copper Wire 44. An insulated heater wire 46 is coiled about the wire 44. One end of the heater wire 46 is soldered or brazed in position as at 48. The lower end of the wire 46 may be grounded to the probe by compressing it in place of the lower end of the wire 44 if such construction is desired. The'upper end of the coil 46 is connected to a cupper wire 50 held out of contact with the probe 36 by an insulator tube 52 of woven glass. The other end of the wire 50 is connected as at 54 to the terminal 30. The wire 50 extends from an opening 56 in the probe and into the chamber 28.

The probe 38 is closed on itself and sealed at one end 58 and at its other end it is compressed to hold an end of a second bimetallic contact element 60 and one end of a wire 62, the other end of the latter being connected as at 64 to the terminal 32. Fiber glass 66 is utilized electrically to insulate the probe 38 from the joined portions of the element 60 and the wire 62.

The stainless steel screw 70 is used to ground the probe 36 to the casing 10 and it is covered by a plastic plug 72 to reduce heat conduction. This screw is located above a threaded plug portion 74 integral with the casing 10 and surrounding the lower end of the insulator member 16. An extension 76 of the plug portion constitutes a protection sleeve or shield for the probes 36 and 38 and defines a space 80 surrounding and separating the probes. Apertures 82 pass through the shield.

In FIGURE 2, a voltage source in the form of a battery is shown at 84 and which is connected by a line 86 to the terminal 30. The terminal 32 is connected by a line 88 and through a lamp 90 to the other side of the battery.

For operation of the switch, let it be assumed that the plug type switch unit is screwed into the wall or jacket of an automobile engine cooling system so that engine coolant normally circulates through the apertures 82 and the space 80 surrounding the corresponding ends of the probes 36 and 38. With the engine running, current normally flows from the battery 84 to the terminal 30 and through the resistance wire 46 and then to ground by way of the stainless steel screw 70. The components are arranged in such a way that immersion of the probes in the coolant liquid removes the heat of the coil 46 faster than it can accumulate in the bimetallic contact 42. With the elements 42 and 60 positioned as shown in FIGURE 1, therefore, no current will activate the lamp 90.

In the event, however, that the engine temperature should unduly arise, the bimetallic elements 42 and 60 are so arranged as to make contact and establish a current through the lamp 90 thereby notifying the operator of the undesirable condition. If coolant temperature is high enough to cause the element 60 to engage the wall of the chamber 26, then a greater rise in coolant temperature will cause the element 42 to make contact with the element 60 and the lamp 90 will be activated. Thus, an excess heat indication is efiected.

If the coolant level lowers and the coolant becomes out of contact with the probes 36 and 38, the elements 42 and 60 will be heated by the coil 46 and make contact at the probes to cause the lamp 90 to be illuminated. An indication of loss of coolant within thirty seconds is found to be practical at any given coolant temperature through the range of 0 F. to 210 F.

FIGURE 3 shows a preferred circuit arrangement which will reduce the power dissipated in the heater coil once the tele-tale lamp 92 has become illuminated. This is to increase the life of the heater coil 46 by reducing the extreme temperature which could be produced by the quantity of energy required to effect adequate time respouse in closing the contacts. In FIGURE 3, a battery 94 is shown connected to ground as at 96 and the other side of the battery is connected by a ballast resistor 98 to the principal resistance coil 46 and a line 100 leading to the lamp 92. The other side of the lam is connected by a line 102 to the bimetallic element 60 and the other bimetallic element 42 is connected to ground as at 70. The current drain of the heater coil 46. is such that only a small voltage is dropped across the line ballast 98 when the switch is open. When the switch closes, however, the power input to the heater coil 46, though small, will be further reduced as a signal is given.

The basic idea of the present invention is that heat is electrically applied .to the switch in such a manner that the presence of coolant removes the heat before it can aecumulate to the temperature level at which the switch closes. When the coolant is replaced by air or saturated vapor in the sensor zone of space or chamber 80, the coefficient of heat conductivity through that zone is greatly reduced. The temperature of switch closure is then readily achieved and the closed switch effects a signal indicating the loss of coolant. Since short time response is desired, the absolute temperature of switch closure is arranged to be a function of absolute ambient coolant temperature so that a change in temperature of a definite number of degrees is required to close the switch at any predetermined temperature.

The fiber glass 66 about the lower end of the bimetallic element 60 could be beryllium oxide or aluminum oxide instead of fiber glass, the main thought being to conduct heat from the coolant through the probe 38 to the bimetallic element 60 and all current to the lamp. A satisfiactory arrangement of the bimetallic elements 42 and 60 is such that a constant gap is maintained between the contact points until the predetermined temperature of closure is arrived at during which the contact of element 42 will catch up and close with the contact of the element 60. y

We claim:

1. A switch for an electrical indicating system including a metal casing, two terminals at one 'end of said casing, insulation between said casing and said terminals, two bimetallic contact elements at said one end and arranged to contact when heated, two heat conducting probes extending from the otherend of said casing, a resistance heater coil in heat exchange. relation with one of said probes, one end of said coil being connected to one of said terminals, the other end of said coil being electrically connected to said casing as a ground, one of said bimetallic contact elements being electrically connected to said one of said probes and in heat transfer relation therewith, the other of said terminals being electrically connected to the other of said contact elements, and said other contact element being electrically insulated from the other of said probes and in heat transfer relation therewith.

2. A switch including a metal casing, two terminals and two bimetallic contact elements being fixed to said casing by insulation and extending in one direction from one end of said casing, two heat conducting probes fixed to said casing by insulation and extending in the opposite direction with end portions out of contact with said casing and insulation, one of said brobes being grounded to said casing and electrically connected to one of said contact elements, each of said probes being connected in heat transfer relation to said bimetallic contact elements, a resistance heater coil in said one probe and connecting one of said terminals to said one probe, the other of said probes being electrically insulated from the other of said bimetallic contact elements and said other contact element being electricaly connected to the other of said terminals.

3. A switch as set forth in claim 2, said metal casing having a threaded plug portion with an inner wall spaced from and encircling said probes, and an end part of said plug portion being apertured to give exposure to said probes.

4. An electrical switch for a cooling medium presence and temperature indicating system, said switch including a metal casing, two terminals and two bimetallic contact elements fixed to said casing by insulation and extending from one end of said casing, two heat conducting probes in heat transfer relation with said contact elements and having ends exposed at the other end of said casing, insulation holding said probes within said casing, one of said probes being grounded to said casing, a resistance heater coil in said one probe and connecting one of said terminals to one of said contact elements and said casing in parallel, and the other of said contact elements being electrically connected to the other of said terminals.

5. A switch as set forth in claim 4, said metal casing being in threaded plug form for attachment to an engine cooling jacket. 2

Hayter et al July 11, 1944 Short et al. Aug. 14, 1956 

1. A SWITCH FOR AN ELECTRICAL INDICATING SYSTEM INCLUDING A METAL CASING, TWO TERMINALS AT ONE END OF SAID CASING, INSULATION BETWEEN SAID CASING AND SAID TERMINALS, TWO BIMETALLIC CONTACT ELEMENTS AT SAID ONE END AND ARRANGED TO CONTACT WHEN HEATED, TWO HEAT CONDUCTING PROBES EXTENDING FROM THE OTHER END OF SAID CASING, A RESISTANCE HEATER COIL IN HEAT EXCHANGE RELATION WITH ONE OF SAID PROBES, ONE END OF SAID COIL BEING CONNECTED TO ONE OF SAID TERMINALS, THE OTHER END OF SAID COIL BEING ELECTRICALLY CONNECTED TO SAID CASING AS A GROUND, ONE OF SAID BIMETALLIC CONTACT ELEMENTS BEING ELECTRICALLY CONNECTED TO SAID ONE OF SAID PROBES AND IN HEAT TRANSFER RELATION THEREWITH, THE OTHER OF SAID TERMINALS BEING ELECTRICALLY CONNECTED TO THE OTHER OF SAID CONTACT ELEMENTS, AND SAID OTHER CONTACT ELEMENT BEING ELECTRICALLY INSULATED FROM THE OTHER OF SAID PROBES AND IN HEAT TRANSFER RELATION THEREWITH. 